Influence of Test Conditions and Test Methods in the Evaluation of Corrosion Inhibitors Used in Pipelines--A Review

Carbon steel is commonly selected as construction material for oil and gas transportation pipelines. However, corrosion will lead to wastage of the metal, either general or locally and also to embrittlement and cracking which can lead to equipment failure. In order to diminish corrosion, inhibitors are added to the system. These are often made up of molecules which are composed of separate hydrophilic head and hydrophobic tail. An ideal inhibitor will rapidly form a thin and effective barrier layer on the metal surface. The layer will resist liquid and gaseous chemicals attack over a wide pH range, be self-healing and the blend components should be cheap, readily available and environmentally acceptable. Adsorption at surfaces is linked predominantly to the electronic structure of the inhibitor molecules and it is well known that slight changes in the chemistry changes its efficiency. In order to improve the performance of corrosion inhibitors and to develop more cost-effective inhibitors a fundamental understanding of the mechanisms is needed. Laboratory methods and the influence of test conditions will be discussed as well as the adsorption behaviour.